The present invention relates to an apparatus for determining the temperature of a substrate, in particular a semiconductor substrate, as well as to an apparatus and a method for the thermal treatment of substrates, in particular semiconductor substrates.
In the art, different apparatuses and methods for thermally treating substrates are known, as well as apparatuses for determining the temperature of a substrate during a thermal treatment.
A known method for thermally treating semiconductor wafers provides for heating of the semiconductor wafers e.g. by means of electromagnetic radiation which is emitted by lamps such as tungsten halogen lamps. For a close loop temperature control of the thermal treatment it is known to determine the temperature of the semiconductor wafer during the treatment by means of a radiometer or pyrometer directed onto the substrate. Since the radiometer, however, typically does not only detect radiation emitted from the semiconductor wafer but also radiation which is reflected at the semiconductor wafer and in some cases radiation which is transmitted through the semiconductor wafer, a differentiation between these radiation fractions is necessary for determining the temperature.
U.S. Pat. No. 5,318,362 describes the so-called ripple technique for such a differentiation, in which a frequency is impressed on the radiation emitted by the lamp via a respective controller. Originally, the AC frequency of the power supply was used and this technique was refined over time and other frequencies were impressed. Changes in the temperature of the semiconductor wafer occur substantially slower in comparison to the impressed frequency. Therefore, the radiation emitted by the semiconductor wafer due to its own temperature does not contain the frequency impressed on the radiation emitted by the lamps and is therefore distinguishable therefrom.
The frequency impressed on the radiation from the lamps now for example enables by means of a respective frequency dependent filtering of the signal of the radiometer, a separation of reflected/transmitted radiation from the radiation emitted by the semiconductor wafer.
In certain applications, however, impressing a frequency via a controller of the lamps is not possible or not desired. This is for example the case when flashbulbs, which are also known as flash lamps, discharge lamps or arc lamps are operated via a bank of capacitors. Such lamps are in particular utilized for short term very rapid temperature increases of surface areas of the substrate and short term annealing processes. Such lamps are typically used in combination with other lamps, such as the above cited ones, which are inter alia used for preheating the semiconductor wafer. During the operation of flash lamps by means of a bank of capacitors, a temperature measurement using the above mentioned technique is, therefore, not possible, since a modulation of the lamp radiation caused by a controller is not provided.